52 BRITISH FOSSIL CRUSTACEA. 
Section oF STRATA BELOW THE BASE OF THE OLD RED SANDSTONE IN THE 
District or LEsMAHAGOW. 
5 a. Coarse conglomerate, chiefly of well-rounded fragments of liver-coloured quartz-rock. This is 
cS E a very persistent band through the whole district. 
‘> < | 6. Red mudstones and shales, with ripple-marks and sun-cracks. 60 to 70 feet. 
3 S e. Grey and green flaggy shales, with hard stone-partings, like portions of the Silurian series, 
2 3 140 feet. 
= ss | d. Red mudstones and shales, like those (4) below the quartzite conglomerate. 500 feet. 
S © | ¢. Red sandstones and fine quartz-conglomerates. 300 feet. 
J. Sandy, flaggy, green stone-bands and shales, with partings of grey and red mudstone passing 
conformably upwards into e. About 130 feet. 
g. Blue, grey, and green shales, sandy mudstones and sandstone bands, becoming more sandy 
towards the top, and more shaly and flaggy towards the bottom. 200 feet. These are the 
Trochus beds; they contain Platyschisma helicites, three species of Lingula, Beyrichia, and 
some undetermined shells. 
h. Hard blue and grey flaggy shales, with occasional bands of calcareous nodules. 350 feet. 
s These are the Pterygotus beds. 
3 7. Hard grey flagstones and bands of hard greywacke. About 500 feet. 
2 k. Grey, blue, and olive shales, becoming more and more interbedded with hard stone-bands 
~ towards the base. About 300 feet. In some of these beds Beyrichia is very abundant ; 
iS" others contain Ceratiocaris, two or three species of Lingula, some shells not yet determined, 
Platyschisma helicites, &c. 
1. Hard bands of greywacke, with shale partings. These form the lowest portion of the Silurian 
series visible in this district. They must be at least 2000 feet thick. Fossils are scarce, but 
an Orthoceras occurs along with plant-like markings and Ceratiocaris. 
The total thickness of Upper Silurian strata in the neighbourhood of Lesmahago cannot 
be less than 3500 feet, and, as the base of the series is nowhere seen, the depth may be much 
more. 
Although the Péerygoti occurring in the dark clay-slates of the Upper Silurian of 
Logan Water and the Nethan River are far inferior in size to the gigantic Pt. anglicus 
from the Lower Old Red Sandstone of Forfarshire and Perthshire, yet for wonderful perfec- 
tion of preservation they can scarcely be rivalled, and certainly not surpassed, by similar 
remains from any other formation. Since the preceding description of P¢. anglicus was 
written, however, I have had the good fortune to visit the Museum of the Natural History 
Society at Montrose (September, 1867), and inspect the magnificent specimen of Pterygotus 
anglicus there preserved, from Lord Panmure’s Quarries at Carmyllie. ‘This unique 
example measures about 3 feet 6 inches in length, 13 inches across the widest segment, 
and is by far the most perfect remain of this species yet met with, having the head united 
